This invention relates to decontamination apparatus and more particularly to apparatus for decontaminating components of nuclear power plants.
During the operation of nuclear power plants and similar apparatus, certain components become exposed to radiation and may develop a thin radioactive film on the surface of the component. From time to time, it is necessary to either inspect or repair these components of the nuclear reactor power plant. During the inspection or repair of the components, it is necessary for working personnel to enter the component or to be stationed in close proximity to the component whereby working personnel may be exposed to radiation emitted from the contaminated component. In some circumstances, the radiation field emitted from these components is such that a worker would receive the maximum permissible radiation dose in less than five minutes of working time. Such a situation means that a given worker may spend only a relatively short amount of time working on the inspection or the repair operation of the nuclear component. Having each worker spend a relatively short amount of time in the repair or inspection procedure, necessitates the use of many workers with each worker working a short time period in order to accomplish the desired procedure. While this may be an acceptable practice for minor inspections or repair procedures, this is not an acceptable practice where there is an extensive inspection or an extensive repair job to be performed. Where the procedure to be performed is a time-consuming procedure, it is likely that an unusually large number of highly trained personnel would be necessary to carry out the task. Such a situation may not only be unacceptable from a financial aspect, but may also be unacceptable from a manpower level aspect. Therefore, what is needed is a decontamination apparatus that reduces the radiation field in components of nuclear reactor power plants so that working personnel may perform operations thereon.
Apparatus has been described in the aforementioned copending application Ser. No. 063,324 for remotely directing a water-grit mixture toward the component to be decontaminated through a nozzle, for example, suspended from the tubesheet of a steam generator. However, the position and tangential velocity of the nozzle in relation to the surface component to be decontaminated must be controlled so that the force of the water-grit mixture is sufficient to provide adequate cleaning and decontamination but not enough to damage the surface of the component. Inadequate cleaning and decontamination may occur if the velocity of the nozzle is too high and/or if the nozzle is too far from the surface of the component to be decontaminated. Damage to the surface of the component to be decontaminated may also result if the nozzle velocity is too low or if the nozzle is too close to the surface of the component to be decontaminated.